two digital LED volt meters using switched ground relay

Discussion in 'General Electronics Chat' started by sdowney717, Nov 21, 2014.

  1. sdowney717

    Thread Starter Member

    Jul 18, 2012
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    [​IMG]

    I have two 2 wire LED digital volt meters to hook up to two 12vdc wet cell batteries.
    I want them switched on and off with the ignition switch.
    the volt meters to monitor the state of charging on each individual battery. The ground is common to both batteries. So I thought to use a cube relay in the ground circuit to turn on and off the meters with the ignition switch.

    Instead of using a relay, is there a simple semiconductor way to do this turning on and off conduction with the common ground circuit? It would have to flow well seeing resistance will drop the voltage affecting the meters.
     
  2. sdowney717

    Thread Starter Member

    Jul 18, 2012
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  3. MikeML

    AAC Fanatic!

    Oct 2, 2009
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    Why do you need a snubber diode around a lamp (or meters)????
     
  4. alfacliff

    Well-Known Member

    Dec 13, 2013
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    why not just switch the power to the volt meters? turn on both when the power is on. the measureing inputs will draw very little current.
     
  5. sdowney717

    Thread Starter Member

    Jul 18, 2012
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    Cant measure the volts independently if just switching on with a single switch.
    consider the boat has 2 engines, 2 independent battery banks. One bank is only for starting, other bank is for house usage, like the two ignition switches .
    Yes, there are two ignition switches, but they both run off the house battery. So then each meter would monitor only the house battery.
    They make 3 wire volt meters that could do that power, ground and measure wires, these happen to be 2 wire voltmeters, just power and ground. I realized after I ordered them the advantage of using the 3 wire meters.
     
  6. sdowney717

    Thread Starter Member

    Jul 18, 2012
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    You dont need a snubber diode for meters, that is just a schematic I found that illustrates the basic idea.
     
  7. sdowney717

    Thread Starter Member

    Jul 18, 2012
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    I just realized, a blocking diode could be put in the on relay circuit. That way both engine ignition switches could power on the LED meters. Otherwise, if you just joined them together, turn on the key, turns on both engines ignition circuits. The way I was thinking of wiring this would only turn on the meters if say the starboard engine was turned on.
     
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